In general, since a nitride semiconductor material including a group V source such as nitrogen (N) and a group III source such as gallium (Ga), aluminum (Al), or indium (In) has excellent thermal stability and a direct transition type energy band structure, the nitride semiconductor material is widely used for a material of a nitride-based semiconductor device, for example, a nitride-based semiconductor light emitting device in an ultraviolet (UV) light range, and a material of a photovoltaic cell.
Since the nitride-based material has a wide energy band gap of 0.7 eV to 6.2 eV, the nitride-based material is widely used as a material of a photovoltaic cell device due to characteristics consistent with those of a solar spectrum. In particular, the UV light emitting device is widely used in various industrial fields, such as light firearms, medical analyzers, therapeutic apparatuses, sterilization systems, water purification systems, and air purification systems and attracts attention as a material usable in general illumination as a future semiconductor illumination light source.